Retrofocus type super-wide angle objective lens

ABSTRACT

A retrofocus type super-wide angle objective lens system usable with a single-lens reflex camera includes a divergent group forming the forward part of the lens system, a quasi-symmetric group disposed behind the divergent group having a diaphragm disposed intermediately thereof, and a convergent group forming the rearward part of the lens system. The satisfactory correction is made both of the negative distortional aberration inherent to the retrofocus type lens and the curvature of meridional plane resulting from the correction of said negative distortional aberration, thereby providing an angle of field ranging from 100* to 110* and a relative aperture of F/5.6 or higher brightness.

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[54] RETROFOCUS TYPE SUPER-WIDE ANGLE OBJECTIVE LENS [30] Foreign Application Priority Data June 5, 1970 Japan ..45/47925 [52] US. Cl ..350/214, 350/176 1 May 16, 1972 M 3,545,845 12/1970 Takahashi ..350/2 l 4 Primary Examiner-John K. Corbin Attorney-Harry G. Shapiro 57 ABSTRACT A retrofocus type super-wide angle objective lens system usable with a single-lens reflex camera includes a divergent group forming the forward part of the lens system. a quasi-symmetric group disposed behind the divergent group having a diaphragm disposed intermediately thereof, and a convergent group forming the rearward part of the lens system. The satisfactory correction is made both of the negative distortionai aberration inherent to the retrofocus type lens and the curvature of meridional plane resulting from the correction of [5 1] Int. Cl. ..G02b said negative distortional aberration, thereby providing an [58] Field of Search ..350/2 l 4, I76 angle of field ranging from 100 to l 10 and a relative aperture of F/5.6 or higher brightness. [5 6] References Cited 7 Claims 33 r g g UNITED STATES PATENTS 3,524,697 8/1970 lsshiki et al. ..350/2 l6 x R|R2R3R4 RsReRrRsRsRm A. riz A3 M5 vdrvdzvdwdwds PATENTEIJMM I 1912 3.663 .095,

sum 1 or a FIG.I

Ll L2 L3 L4 L5 A. n2 n2 M5 vdrvdzvdsvawds FIG. 2

INVENTOR. zKuo nos! ATTORNfY PATENTEDMAY 16 m2 3.663.095

SHEET 2 BF 8 (ABERRATION CORVES FOR f=|5.4)

FIG. 30 FIG. 3b FIG. 36 FIG. 3d

SP ERICAL ABE'ERAWN ASTIGMAT'SM DIST RTIONAL ASTIGMATISM SINE CONDITION 5 WWW FOR fl- /ao 500 llI LATERAL SPHERICAL ABERRATION COMA FOR 35 COMA FOR 55 I N" "EM TOR 1 K (J 0 MO RI ATTORNEY PATENTEnIAns I972 SHEET 3 BF 8 FIG. 5b FIG. 50

FIG. 5a

L AN. M 0 RM F 1 m o o o o 5 O 5 5 5 J 5 4 3 2 M E O T A 5 .M. m n m A w 5 N Mm F C m 0 ER llll ll HHI Hum F ATTORNEY PATENTEDm 16 I972 3. 663 095 SHEET UF 8 FIG. 5d

COMA

ML-3 I'Ql LATERAL SPHERICAL ABERRATION 'COMA FOR 35 COMA FOR 55 \L? L L9 LIO Lll LI2 ATTORME Y PATENTEDm 16 m2 SHEET 7 OF 8 (ABERRATION CORVES FOR f=l8.4) F I6. I00

FIG. IQb, FIG. IOC FIG. IOd SPHERICAL DISTORTIONAL ASTIGMATISM ABERRATION ASTIGMATISM sms CONDITION ABERRAT'ON FOR V30 1 l I l FlGglOe 5s w- I I -0.1

- LATERAL SPHERICAL ABERRATION COMA FOR 30 COMA FOR 50 INVENTOR. I K U0 MORI ATTORIyEY I PATENTEDMAHB I972 3.663.095

Q'LIOLII L12 L'rLe'L Ll L2 L3 L4 L6 FIG. I20 FIG. l2b FIG. l2c

SPHERICAL DISTORTIONAL ASTIGMATISM fi ggggg o ABERRATION L IQl LO. 1 LATERAL SPHERICAL ABERRATION COMA FOR 30 COMA F0R150 A TTORNEY BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to a retrofocus type super-wide angle objective lens having an angle of field ranging from 100 to 1 and more particularly to a retrofocus type objective lens having a long back focus (hereinafter simply referred to as B.f.) which is usable with a single-lens reflex camera.

2. Description of the Prior Art In the retrofocus type lens system. the arrangement of the lens group forming the forward part of the lens system makes a critical factor inproviding a super-wide angle of field. Especially, the foremost lens of the group decisively governs the performance of the entire lens system.

For example, if a positive lens is used as the foremost lens,

' an oblique light beam incident on the positive lens will of course leave it at an angle of exit greater than the angle of incidence and this will increase the aberration of the oblique light beam or the curvature of meridional plane. Such aberration tends to result in an over-correction in the peripheral region of the image field while it tends to cause an under-correction in the vicinity of 80 percent of the image field. This is because in the retrofocus type lens system a light beam having a greater angle of incidence is incident at a remoter point from the optical axis so that it is subjected to a greater refraction provided by the peripheral region of the positive lens. If a negative lens is used as the foremost lens, the curvature of meridional plane in the peripheral region of the image field V will be reduced while the negative distortional aberration will be increased. For example, the so-called fish-eye lens which is typical of the super-wide angle lens has an angle of field as great as approximately 180, but this lens by its very nature requires no correction of the distortional aberration and the curvature of meridional plane is small over the entire image field. However, in the super-wide angle lens as an ordinary J photographic objective lens, the distortional aberration must also be corrected and this involves the requirement that a positive lens for correcting the negative distortional aberration be added to the lens system, especially to the divergent group forming the forward part thereof. The tendency to aberration as seen in the described lens system whose foremost lens is a positive lens is also the case with the lens system whose foremost divergent group includes a positive lens, and therefore it is impossible to provide a good meridional plane by the technique of simply adding a positive lens. Especially, in order to obtain a super-wide angle of field, the refractive power of the divergent group must be considerably great and this in turn requires the positive lens added thereto to have a great refractive power. Thus, a good meridional plane becomes more and more difficult to obtain.

The described technique of the prior art encounters another problem. In order to increase B.f. in the retrofocus type lens system, it is usually the practice to increase the refractive power of the divergent group forming the forward part of the lens system. However, a simply increased refractive power may result in an increased negative distortional aberration as described above and this gives rise to the need to correct such distortional aberration as well as to correct the curvature of meridional plane resulting from the correction of that distortional aberration. Thus, it becomes difficult to simply utilize the aforesaid known technique.

Further, a retrofocus type lens, especially a lens system having a long B.f., tends to produce comas of different natures in the peripheral and intermediate regions of the image field. This will be attributable to the fact that the peripheral region of the image field is intensely affected by the meridional plane while the intermediate region is intensely affected by the sine condition. Moreover, if it is desired to have a greater quantity of light reach the peripheral region of the image field, the beam of incident light having a great angle of skew will grow thicker, and when it is refracted in the peripheral region of the divergent group, the inner ray in the beam of light leaving at a relatively small angle of exit and the outer ray leaving at a greater angle of exit are asymmetrical about the main ray, thereby deteriorating the coma.

SUMMARY OF THE INVENTION It is a first object of the present invention to provide a retrofocus type super-wide angle objective lens in which good correction is made both of the negative distortional aberration inherent to the retrofocus type lens system and the curvature of meridional plane resulting from the correction of said negative distortional aberration and which has an angle of field in the range of to 1 10 and a relative aperture of W5 .6 or higher brightness.

It is a second object of the present invention to provide an objective lens whose B.f. is about 2 to 2.5 times as great as its focal length.

It is a third object of the present invention to provide an objective lens which can have a greater quantity of light in the peripheral region of the image field and whose coma is satisfactorily corrected over the entire image field.

These objects and other features of the present invention will become more apparent from the following illustrative description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of the lens system ac- I tion, (a) showing the spherical aberration and sine condition,

(b) the astigmatism, (c) the distortional aberration, (d) the astigmatism for B 1/30, and (e) the coma.

- FIG. 4 is a longitudinal sectional view of the lens system according to Example II of the present invention.

FIGS. 5(a), (b), (c) and (:1) illustrate the various aberration curves for f 15.4 in Example II, (a) showing the spherical aberration and sine condition, (b) the astigmatism, (c) the distortional aberration and (d) the coma.

FIG. 6 is a longitudinal sectional view of the lens system according to Example III of the present invention.

FIGS. 7(a), (b), (c) and (d) illustrate the various aberration curves for f 16.4 in Example III, (a) showing the spherical aberration and sine condition, (b) the astigmatism, (c) the distortional aberration and (d) the coma.

FIG. 8 shows, in longitudinal cross section, the lens system according to Example IV of the present invention.

FIG. 9 is an enlarged sectional view showing the rearward portion of the lens system shown in FIG. 8.

FIGS. 10(a), (b), (c), (d) and (e) illustrate the various aberration curves for f 18.4 in Example IV, (a) showing the spherical aberration and sine condition, (b) the astigmatism, (c) the distortional aberration, (d) the astigmatism for B 1/30, and (e) the coma.

FIG. 11 is a longitudinal sectional view of the lens system according to Example V of the present invention.

FIGS. 12(a), (b), (c) and (d) illustrate the various aberration curves for f 18.4 in Example V, (a) showing the spherical aberration and sine condition, (b) the astigmatism, (c) the distortional aberration and (d) the coma.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Description will now be made of various examples of the present invention and throughout the description use will be made of the following symbols.

f: focal length of the entire lens system.

R radius of curvature of each lens surface or cemented lens surface.

d center thickness of each lens and air spacing between adjacent lenses.

n refractive index of each lens for helium d spectro-ray.

ud dispersive power of each lens for helium d spectro-ray.

Various suffix numbers added to these symbols represent the order of arrangement as viewed in the direction of incidence, which arrangement takes place in accordance with the natures represented by the respective symbols.

Referring first to FIGS. 1 to 3, an objective lens system according to Example I of the present invention is shown which has a field angle of 110 and a relative aperture of F/5. This lens system includes a first and a second component L, and L each of which comprises a negative single meniscus lens having the convexsurface thereof for direction toward the object.

These first and second components are followed by a third component L comprising a positive single meniscus lens whose convex surface also is for the direction toward the object, a fourth and a fifth component L and L, each comprising a negative single meniscus lens whose convex surface also is for direction toward the object, and a sixth component L comprising a positive cemented meniscus lens assembly which consists of three lenses, i.e. a biconcave lens, a biconvex lens and a negative meniscus lens having the concave surface thereof for direction toward the object, these three lenses being cemented together. The positive cemented meniscus lens assembly as a whole has a forward-looking concave surface. Behind the sixth component L is disposed a seventh component L comprising a negative single meniscus lens whose convex surface is for direction toward the object. An eighth component L follows which comprises a positive cemented lens assembly consisting of a biconvex lens and a negative lens joined together. The positive cemented lens assembly as a whole has the convex surface thereof facing forward, and it is followed by a diaphragm D, which in turn is followed by a ninth component 1., comprising a positive single lens having the convex surface thereof looking rearward or toward the image plane. Behind the ninth component L there is disposed a 10th component L, comprising a single biconcave lens, which is followed by an I lth component L,, comprising a positive single meniscus lens having a forward-looking concave surface. A 12th component L comprising a positive single lens having a rearward-looking convex surface terminates the lens system.

Functionally, the components L, to L constitute a divergent group, the components L to L,, a quasi-symmetric group relative to the diaphragm D, and the last component L, a convergent group.

R, and R of the first component L, and R and R, of the second component L, are in the relations as shown below:

l.3 (R,/f) 2.5, l.2R R;, 2R (ll) These two conditions are meant to prevent to some degree the deterioration of the meridional plane which would result from the refraction provided by the positive lenses included in the divergent group.

In order to provide a super-wide angle of field, it is unavoidable that the refractive power of the divergent group must be considerably great as described above, whereas the negative distortional aberration resulting from such dispersion must in turn be minimized. For this purpose, according to the present invention, the first half of the divergent group is separated into two negative components L, 'and L whose respective forward-looking convex surfaces R, and R, are increased in curvature so that an incident light beam having a great angle of skew on the respective components L, and L are formed in such a manner that the curvature difference is as small as possible between the surfaces of incidence and exit. This helps to reduce the negative distortional aberration produced in each of these components, which in turn permits the positive component L to correct such negative distortional aberration to a relatively small refractive power, thus preventing the deterioration of the meridional plane to some degree.

R, and R of the fourth component L, and R, and R,,, of the fifth component L, are in the following relations:

(III) proved since the meridional These two conditions are meant to separate the latter half of the divergent group into two negative components L,, L, so as to further improve the curvature of meridional plane and distortional aberration which have already been corrected to some degree by the previously shown conditions (I) and ll The significance of the conditions (III) and (IV) is entirely the same as that of the conditions (I) and (II). It will be noted I that the numerical values in the conditions (III) and (IV) are reduced to about one half of those in the conditions (I) and (II), and this is because the incident light beam is refracted to be close to the optical axis by the third component L interposed between the first and latter halves of the divergent group, whereby the radii of curvature of the fourth and fifth components L, and L, necessarily become smaller than those of the first half of the divergent group.

In this way, the negative refractive power is reduced and divisionally allotted and moreover, there is added a positive component having a relatively small refractive power, so that the incident light beam as a whole cannot be subjected to a great positive refractive power. As a result, it is possible to decrease the curvature of meridional plane.

If among the conditions (I) to (IV) the inequalities related to the curvature difference (those given on the right-hand side of the conditions) are not satisfied, it will be apparent that the negative refractive power will become greater to thereby increase the negative distortional aberration, and this in turn would require that the refractive power of the positive component be increased in order to compensate for the increased negative distortional aberration. Such a vicious circle would make it impossible to provide the good results as described above. If the inequalities related to the inner sides of the meniscus lenses are not satisfied, a predetermined B.f. as a retrofocus type lens system could not be obtained.

In order to obtain a great B.f., the sixth component L is constituted by a cemented lens assembly, and the relation between the refractive indices n, and n; in the regions on the opposite sides of the cemented forward surface R of that lens and the relation between the center thicknesses of the respective lenses in this component are set as follows:

"a "1 l2 is u Further, the relation between R and R of the seventh com- Thus, a great B.f. can be obtained.

The conditions (V) and (VI) are intended to maintain a positive refractive power in the sixth component L as a whole and at the same time to direct light through the component in the divergent direction so as to enable the light to leave that component at points remote from the optical axis. More specifically, the condition (V) is useful in that light can be directed upwardly to a greater extent without the need to increase the curvature of the cemented surface R but rather by utilizing the difference in refractive index between the lenses of the component L to eliminate the undesirable influence resulting from a great curvature. In addition, the condition (VI) provides a great value of 11, d so as to provide points of exit remote from the optical axis. This is due to the fact that if the points of incidence are higher than the points of exit, B.f. can be increased as if a divergent component were used.

Further, the condition (VII) is intended partly to compensate for the negative refractive power of the divergent group L,-I since the seventh component L closely adjacent to the diaphragm D does not significantly harm the distortional aberration even if the negative refractive power of the component L is increased. Of course, the condition (VII) is also meant to increase B.f.

The numerical values in the condition (VII) are about half of those for the latter part of the divergent group because the points of incidence are further closer to the optical axis.

The coma in the peripheral region of the image field is implane is improved by the conditions (1) to '(VII), while the coma in the intermediate and other regions tends to take place generally in the positive (VII) sense because it is related to the sine condition as mentioned previously. For this reason, the center thickness d of the rearmost twelfth component I.., is made extremely great as shown below:

0.4f d,,, 0. 7f VIII) I Thereby the sine condition is improved.

Thus, the coma can be corrected satisfactorily over the entire image field. but care should be taken in selecting the value of the center thickness d because too great a value for the center thickness d causes the distortionai aberration to displace in the negative sense.

In this way, with the improvement of the coma, the quantity of incident light can be greatly increased, amounting to, say, 190 percent of the aperture as measured in a first tangential plane, and 20.6 percent as measured by cos 4 theory.

Also, the extremely wide angle of field tends to result in an over-correction of the sagittal plane in the peripheral region of the image field. Therefore, in the quasi-symmetric group, the following conditions are set up to improve the sagittal plane.

For the correction of the out-axial chromatic aberration, the dispersive powers on the opposite sides of the rearward cemented surface R, of the sixth component L are set thus:

vd, vd and the similar factors on the opposite sides of the cemented surface R of the eighth component L; are set thus:

vd, vd,, Thus, good correction of such chromatic aberration can be achieved. 7

The data of Example I will now be shown.

EXAMPLE I (FIGS. l-3) n, 1.52 vd I 70.1

Lens Curvature Curv- Distorsurface of mm ature of tional order Spherical gential sagittal aber- No. aberration Coma image image ration 1 11 111 IV V 1 0.009 0.009 0.167 0.150 0.146 2 0.065 0.010 0.216 0.212 0.034 3 0.037 0.024 0.197 0.165 0.109 4 0.144 0.003 0.213 0.213 0.004 5 0.084 0.045 v 0.212 0.163 0.087 6 0.000 0.001 0.052 .0.031 0.529 7 0.083 +0.048 0.374 0.318 0.184 8 1.080 0.104 0.502 0.483 0.046 9 0.665 0.115 0.396 0.356 0.062 10 3.092 0.287 0.587 0.533 0.050 1 1 0.222 0.204 0.539 0.161 0.149 12 8.299 0.658 0.290 0.186 0.015 13 0.007 0.002 0.002 0.001 0.000 14 0.724 0.309 0.680 0.417 0.l78 15 5.431 0.848 0.713 0.448 0.070 16 144.916 2.066 0.832 0.774 0.011 17 95.385 4.675 1.129 0.671 0.033 18 0.090 0.010 0.005 0.002 0.003 19 0.015 0.028 0.161 0.054 0.102 20 0.015 0.028 0.162 0.054 0.102 21 98.553 3.203 0.780 0.571 0.019 22 68.738 2.043 0.698 0.577 0.017 23 16.792 -4.430 3.714 l.377 -0.363 24 1.331 0.724 1.121 0.332 0.181 25 21.626 0.237 0.448 0.442 0.005 26 0.002 0.006 0.071 0.031 0.100 27 21.331 0.470 0.299 0.278 0.006 I 2.274 0.029 0.020 0.114 0.183

FIGS. 4 and 5 show Example 11 of the present invention. In

0 this Example, the distortional aberration present in the forego- EXAMPLE 11 (FIGS 4-5) f= 15.4 B1. 38.04 F/5.6 Angle offield: 110

R,: revolution-symmetric non-spherical surface. R,,, R,', d d,,', n,,: filters. R, 48.0

d,=3.1 n,= 1.732 vd,=53.2 R, 30.9 d 7.4

d,,=2.0 n,= 1.732 vd,=53.2 R, 30.6

d, 4.8 R, 45.6 d =7.6 n;=l.7 vd,=47.9 R|=310.5

d =1.0 n4=1.8411 d,=4,3 3 Rs: 14.9

ds=3.0 R, 20.9

d,,=1.0 n,=1.8411 vd,=43.3 R,,, 13.9

d,,, 5.6 R0 cc d =1.2 n,,=1.51743 Ro' do 1.0

R, 255.0 d,,=1.1 n,=l.841l vd,=43.3 R 12.65

11,, 10.0 n,= 1.54072 vd, 47.2 R 10.8 d,,,= 2.0 n,,= 1.53996 id, 59.7

d 1.0 n, 1.6968 vd, 55.6 R,,,= 8.5

d,,=1.05 n 1.58313 11d 59.3 ID

d 6.4 n 1.58065 11d 37.1 R =12.12

d 1.1 n 1.86074 ud 23.1 R 34.65

The following shows the configuration of the non-spherical surface, in which the effective radius of R is 33.5.

R Amount of deviation 2 from the spherical surface of 46.0.

0.000 5 0.0033 Height I from 0.0090 optic axis FIGS. 6 and 7 show Example 111 of the present invention, in which the distortional aberration present in Example 1 is corrected to a further degree without using the non-spherical surface. The angle of field is slightly reduced to 106.

EXAMPLE 111 (FIGS. 6-7) In Examples IV and V as shown in FIGS. 8 to 12, the number of lenses in use is reduced for economy of manufacture. Both of these examples have a high performance such as 100 angle of field and a relative aperture in the range of F /3.5 to F/4. As compared with Examples 1 to 111 shown in FIGS. 1 to 7, these alternative examples reduce the number of lenses in the latter half of the divergent group and in the quasi-symmetric group.

More specifically, in Examples 1V and V, the latter half of the divergent group is composed of two components. i.e. a fourth component L comprising a negative single meniscus lens having a forward-looking convex surface, and a sixth component 1. comprising a composite lens formed by a biconcave lens and a biconvex lens cemented together, the composite lens as a whole having the concave surface thereof for direction toward the object.

The divergent groups of Examples IV and V differ from those of Examples 1 to III in that the fifth component 1. is eliminated and that the rearward meniscus lens is eliminated in the sixth component L The quasi-symmetric group in Examples IV and V is constituted by an eighth component L and a ninth component L with a diaphragm D interposed therebetween, the component L comprising a positive single lens having a forwardlooking convex surface and the component L comprising a positive single lens having a rearward-looking convex surface.

As compared with Examples 1 to 111, the quasi-symmetric group in either of Examples 1V and V differs in that the rearward negative lens is omitted in the eighth component L 1 In such a lens system, a long B.f. can hardly be obtained simply by replacing the fourth and fifth components L and 1. of Examples 1 to 111 with a single component. Therefore, R and R, of the component L are set to satisfy the following relations:

0.6 R,,' f) o.s, 1.5R,,' R,' 2.5R,' Thus, the negative refractive power is increased, and the fact that the angle of field smaller than that in Examples 1 to 111 results in a smaller out-axial chromatic aberration permits the omission of the achromatic cemented surfaces of the sixth and eighth components L and L used in Examples Ito 111. Here are the detailed data of Examples 1V'and V.

EXAMPLE 1V (FIGS. 8-10) f== 18.4 13.1. 37.52 PM Angle of field: 100 R, 42.0

d,= 1.8 11 =1.ss 17d, 55.6 R. 25.5

a, 5.0 11,=1.62041 11d,= 60.3 R, 250.0

11,'= 1.0 n,'=l.6968 11d.'=55.s R,,' 12.4

Rs (omitted) d, (omitted) n, (omitted) vd, omitted) R (omitted) din (omitted) R,,'=200.0

d ,=2.0 n.,'=l .77279 vd,= 49.5 R.,'= 12.3

d,,'=12.0 n-,'=l.589 vd,'= 48.6 R,,'=-2s.0

- d (omitted) R (omitted) a 0.1 n, (omitted) vd, (omitted) R 23.8

d 1.0 n, =1 .67025 vd 57.5 R... 10.1

d 5.95 n '=1.S8065 ud, '=37.l R on dis 1 Omitted) R, (omitted) d,,= 1.5 n (omitted) vd (omitted) R20: 2:

d,,,'= 2.0 n ,'=1.58065 vd,,'=37.1 R,,=l4.3

d 3.1 n =1.86074 vd =23.) R 50.7 s

d 0.9 R =-3s.s

d,.= 2.5 n,.=l.51823 vd =59.0 R =1 1.8 d 0.1

d,.,= 8.5 n,,=1.5567l 11d =58.5 R 19.337

Lens Curvature Curv- Distorsurface Sph r l of tanature of tional order aberration gential sagittal aber- No. Coma image image ration 1 I1 111 IV V I 0.020 0.018 0.229 0.196 0.177 2 0. 155 0.004 0.271 0.271 0.007 3 0.089 0.042 0.259 0.219 0.103 4 0.400 0.018 0.299 0.297 0.014 5 0.213 0.078 0.263 0.205 0.075 6 I 0.001 0.006 0.139 0;065 0.436 7' 0.178 0.079 I 0.414 0.342 0.153 8 3.780 0.660 0.955 0.725 0.127 9 (omitted) 10 (omitted) l 1' 0.102 0.137 0.513. 0.144 0.194 12 4.585 0.530 -0.282 0. 159 0.018 13' 0.055 0.047 0.361 0.283 0.238 14 (omitted) 15 2.883 0.619 0.709 0.443 0.095 16 68.879 1.036 0.778 0.747 --0.01 1 17' 40.836 2.856 1.014 0.614 0.043 18' 0.029 0.050 0.253 0.084 0. 144 19 (omitted) 20' +0.029 0.050 0.256 0.085 0.146 21' 42.921 4.353 1.797 0.914 0.093 22 30.000 2.199 1.067 0.744 0.055 23 6.425 2.685 3.533 1.290 0.539 24 0.091 0.166 0.745 0.140 0.255 25 13.209 0.011 0.532 0.532 0.000 26 0.000 0.000 0.002 0.007 0.145 27 18.215 1.202 0.579 0.420 0.028 2 4.587 0.471 0.096 0.148 0.174

EXAMPLE V FIGS. 11-12) f= 18.4 8.1". 37.54 F/3.5 Angle offield: 100 R, 42.0

d, 2.0 n, =1.6935 Ild 50.6 R, 28.0

d. 3.8 7.8 3 a. 1.8 n, =1.6968 P d, 55.6 R 25.5

a. 4.5 a, 5.0 n. =1 .62041 m1, 57.5

R (omitted) d (omitted) As described, the present invention provides a retrofocus type super-wide angle objective lens in which aberrations such as astigmatism and coma are corrected satisfactorily over the entire image field in spite of the extremely wide angle of field.

What is claimed is:

l. A retrofocus type lens system comprising the combination of:

i. a divergent group forming the forward part of the lens system and including at least:

a. a first pair of divergent components disposed at the foremost end of the lens system, each of said first pair of divergent components comprising a negative single meniscus lens having the convex surface thereof for direction toward object, I

. a first convergent component disposed behind said first pair of divergent components and comprising a single meniscus lens having the convex surface thereof for direction toward object,

c. a second pair-of divergent components disposed behind said first convergent component, each of said second pair of divergent components comprising a negative single meniscus lens having the convex surface thereof for direction toward the object, and

d. a second convergent component disposed behind sai second pair of divergent components and comprising a cemented lens assembly consisting of a biconcave lens, a biconvex lens and a negative meniscus lens disposed in the named order in the rearward direction and joined together, said negative meniscus lens having the concave surface thereof for direction toward object, said cemented lens assembly as a whole having the concave 1 surface thereof for direction toward the object;

. ii. a quasi-symmetric group disposed behind said divergent group and having a diaphragm disposed intermediately, said quasi-symmetric group comprising at least:

e. a third divergent component forming the foremost part of said quasi-symmetric group and comprising a single meniscus lens having the convex surface thereof for direction toward object,

f. a third convergent component disposed behind said third divergent component and just before said diaphragm, said third convergent component comprising a cemented'lens assembly comprising a biconvex lens and a divergent lens disposed in the named order in the rearward direction and joined together, said cemented lens assembly as a whole having the convex surface thereof for direction toward the object,

g. a fourth convergent component disposed just behind said diaphragm and comprising a single lens having the convex surface thereof for direction toward the image toward the image in such a manner that said convex surface is substantially symmetrical with said forwardlooking convex surface of said third convergent component about said diaphragm,

a fourth divergent component disposed behind said fourth convergent component and comprising a biconcave lens, and

i. a fifth convergent component disposed behind said fourth divergent component and comprising a single meniscus lens having the convex surface thereof looking rearward in such a manner that said convex surface is substantially symmetrical with said forward-looking convex surface of said third divergent component about said diaphragm; and

iii. a convergent group forming the reannost part of the lens system and comprising at least one component consisting of a positive single lens having the convex surface thereof for direction toward the image. 2. A retrofocus type lens system according to claim 1, which has the data as follows:

where f denotes the focal length of the entire lens system, R denotes radius of curvature of each lens surface, d denotes center thickness of each lens and air spacing between adjacent lenses, n subscript denotes refractive index of each lens for helium d spectro-ray, and mi denotes dispersive power of each lens for helium d spectre-ray.

3. A retrofocus type lens system according to claim 1, which has the data as follows:

f- 15.4 8.1. I 38.04 F/5.6 Angle of field: R revolution-symmetric non-spherical surface. R1,, R1,, d d n filters. R, I 48.0

d,=3.l 11,=1.732 vd, 53.2 R, I 30.9

d, I 7.4 R; I 43.6

d =2.0 n,= 1.732 vd,=53.2 R, I 30.6

a, 4.8 R; I 45.6

d, 7.6 '1 1.7 vd 47.9 R, I 310.5 d, 0.1 R, I 24.2

11,=1.o 11.=1.8411 1111,=43.3' R, I 14.9

d,,=1.0 n,=1.8411 v11,=43.3 R 13.9

d 5.6 R0 on d 1.2 n,,= 1.51743 R1, 5 m

11,,= 2.0 11,, 1.53996 1111,, 59.7 RH l 8.8

d, 7.0 11,, 1.52 1111,, 70.0 R,,= 20.5s4

where f denotes the focal length of the entire lens system, R denotes radius of curvature of each lens surface, d denotes center thickness of each lens and air spacing between adjacent lenses, n denotes refractive index of each lens for helium d spectro-ray, and 11d denotes dispersive power of each lens for helium d spectre-ray.

4. A retrofocus type lens system according to claim 1, which has the data as follows:

f= 16.4 175.6 Angle 111116111. 106 R, 39.7

where f denotes the focal length of the entire lens system, R denotes radius of curvature of each lens surface, d denotes center thickness of each lens and air spacing between adjacent lenses, n denotes refractive index of each lens for helium d spectre-ray, and vd denotes dispersive power of each lens for helium d spectre-ray.

5. A retrofocus type lens system comprising the combination of:

i. a divergent group forming the forward part of the lens system and including at least:

a. a first pair of divergent components disposed at the foremost end of the lens system, each of said first pair of divergent components comprising a negative single meniscus lens having the convex surface thereof for direction toward an object,

b. a first convergent component disposed behind said first pair of divergent components and comprising a single meniscus lens having the convex surface thereof for direction toward the object,

c. a second divergent component disposed behind said first convergent component and comprising a single meniscus lens having the convex surface thereof for direction toward the object, and

d. a second convergent component disposed behind said second divergent component and comprising a cemented meniscus lens assembly consisting of a biconcave lens and a biconvex lens disposed in the named order in the rearward direction and joined together, said cemented meniscus lens assembly as a whole having the concave surface thereof for direction toward the object;

ii. a quasi-symmetric group disposed behind said divergent group and having a diaphragm disposed intermediately, said quasi-symmetric group comprising at least;

- e.'a third divergent component forming the foremost part of said quasi-symmetric group and comprising a single meniscus lens having the convex surface thereof for direction toward object,

f. a third convergent component disposed behind said third divergent component and just before said diaphragm, said third convergent component comprising a single lens having the convex surface thereof for direction toward the object,

g. a fourth convergent component disposed just behind said diaphragm and comprising a single lens having the convex surface thereof for direction toward the image in such a manner that said convex surface is substantially symmetrical with said forward-looking convex surface of said third convergent component about said diaphragm,

h. a fourth divergent component disposed behind said fourth convergent component and comprising a biconcave lens, and

i. a fifth convergent component disposed behind said fourth divergent component and comprising a single meniscus lens having the convex surface thereof for direction toward the image in such a manner that said convex surface is substantially symmetrical with said forward-looking convex surface of said third divergent component about said diaphragm; and

iii. a convergent group forming the rearmost part of the lens system and comprising at least one component consisting of a positive single lens having the convex surface thereof for direction toward image.

6. A retrofocus type lens system according to claim 5, which has the data as follows:

= 18.4 B.f. 37.52 PM Angle of field: l00

d. 2.0 n, l.6968 m1. 55.6 R 27.9

d 5.0 71,, 1.6204! vd 60.3 R 250.0

d 1.0 71 1.6968 vd" 55.6 R. 12.4

(1,. 7.0 R, (omitted) d (omitted) :1 (omitted) ud, (omitted) R (omitted) d (omitted) R,,'=200.0

d (omitted) RH (omitted) d 0.1 n (omitted) m1 (omitted) R" 23.8

d,,- 10 11. 1.67025 vd, 57.5 R 10.1

d (omitted) R" (omitted) d 3.2 n 1.86074 vd,,= 23.1 R 50.7

d,.= 2.5 n 1.51823 ud 59.0 12,, =1 l.8

where f denotes the focal length of the entire lens'system. R denotes radius of curvature of each lens surface, d denotes f= 18.4 B.f. 37.54 F/3.5 Angle of field: 100 R, 42.0

d 2.0 n 1.6935 vd, 50.6 R 28.0

d 1.8 u 1.6968 ud 55.6 R 25.5 I

d,= 5.0 n;,= 1.62041 vd =57.5 R, 280.0

d, 1.0 11 1.6968 11d. 55.6 R,.' 12.4

d, 7.0 R (omitted) d, (omitted) n5 (omitted) yd, (omitted) R (omitted) d (omitted) R,,'=200.0

d (omitted) R (omitted) vd, (omitted) l dll (omitted) where f denotes the focal length of the entire lens system, R denotes radius of curvature of each lens surface, d denotes center thickness of each lens and air spacing between adjacent lenses, n denotes refractive index of each lens for helium d spectro-ray, and 1 d denotes dispersive power of each lens for helium d spectre-ray. 

1. A retrofocus type lens system comprising the combination of: i. a divergent group forming the forward part of the lens system and including at least: a. a first pair of divergent components disposed at the foremost end of the lens system, each of said first pair of divergent components comprising a negative single meniscus lens having the convex surface thereof for direction toward object, b. a first convergent component disposed behind said first pair of divergent components and comprising a single meniscus lens having the convex surface thereof for direction toward object, c. a second pair of divergent components disposed behind said first convergent component, each of said second pair of divergent components comprising a negative single meniscus lens having the convex surface thereof for direction toward the object, and d. a second convergent component disposed behind said second pair of divergent components and comprising a cemented lens assembly consisting of a biconcave lens, a biconvex lens and a negative meniscus lens disposed in the named order in the rearward direction and joined together, said negative meniscus lens having the concave surface thereof for direction toward object, said cemented lens assembly as a whole having the concave surface thereof for direction toward the object; ii. a quasi-symmetric group disposed behind said divergent group and having a diaphragm disposed intermediately, said quasisymmetric group comprising at least: e. a third divergent component forming the foremost part of said quasi-symmetric group and comprising a single meniscus lens having the convex surface thereof for direction toward object, f. a third convergent component disposed behind said third divergent component and just before said diaphragm, said third convergent component comprising a cemented lens assembly comprising a biconvex lens and a divergent lens disposed in the named order in the rearward direction and joined together, said cemented lens assembly as a whole having the convex surface thereof for direction toward the object, g. a fourth convergent component disposed just behind said diaphragm and comprising a single lens having the convex surface thereof for direction toward the image toward the image in such a manner that said convex surface is substantially symmetrical with said forward-looking convex surface of said third convergent component about said diaphragm, h. a fourth divergent component disposed behind said fourth convergent component and comprising a biconcave lens, and i. a fifth convergent component disposed behind said fourth divergent component and comprising a single meniscus lens having the convex surface thereof looking rearward in such a manner that said convex surface is substantially symmetrical with said forward-looking convex surface of said third divergent component about said diaphragm; and iii. a convergent group forming the rearmost part of the lens system and comprising at least one component consisting of a positive single lens having the convex surface thereof for direction toward the image.
 2. A retrofocus type lens system according to claim 1, which has the data as follows: f 15.4 B.f. 38.06F/5 Angle of field: 110*R1 46.0 d1 3.1 n1 1.732 Nu d1 53.2 R2 30.9 d2 7.4 R3 43.6 d3 2.0 n2 1.732 Nu d2 53.2 R4 30.6 d4 4.8R5 45.6 d5 7.6 n3 1.7 Nu d3 47.9R6 310.5 d6 0.1 R7 24.2 d7 1.0 n4 1.8411 Nu d4 43.3R8 14.9 d8 3.0 R9 20.9 d9 1.0 n5 1.8411 Nu d5 43.3R10 13.9 d10 6.6 R11 -255.0 d11 2.8 n6 1.8411 Nu d6 43.3R12 12.2 d12 10.0 n7 1.54072 Nu d7 47.2R13 -10.8 d13 2.0 n8 1.53996 Nu d8 59.7R14 -18.9 d14 0.2 R15 20.0 d15 1.0 n9 1.6968 Nu d9 55.6R16 8.5 d16 2.3 R17 12.8 d17 3.8 n10 1.58065 Nu d10 37.1R18 -14.0 d18 1.0 n11 1.58313 Nu d11 59.3R19 Infinity d19 1.7 R20 Infinity d20 5.62 n12 1.58065 Nu d12 37.1R21 -12.1 d21 2.3 R22 -13.8 d22 0.65 n13 1.86074 Nu d13 23.1R23 34.4 d23 0.65 R24 -77.0 d24 2.0 n14 1.44628 Nu d14 67.2R25 -10.8 d25 0.1 R26 466.0 d26 7.6 n15 1.52 Nu d15 70.1R27 -19.679 where f denotes the focal length of the entire lens system, R denotes radius of curvature of each lens surface, d denotes center thickness of each lens and air spacing between adjacent lenses, n subscript denotes refractive index of each lens for helium d spectro-ray, and Nu d deNotes dispersive power of each lens for helium d spectro-ray.
 3. A retrofocus type lens system according to claim 1, which has the data as follows: f 15.4B.f. 38.04 F/5.6 Angle of field: 110* R1: revolution-symmetric non-sphericalsurface. R0, R0'', d0, d0'', n0: filters. R1 48.0 d1 3.1 n1 1.732 Nu d1 53.2R2 30.9 d2 7.4 R3 43.6 d3 2.0 n2 1.732 Nu d2 53.2R4 30.6 d4 4.8 R5 45.6 d5 7.6 n3 1.7 Nu d3 47.9R6 310.5 d6 0.1 R7 24.2 d7 1.0 n4 1.8411 Nu d4 43.3 R8 14.9 d8 3.0R9 20.9 d9 1.0 n5 1.8411 Nu d5 43.3R10 13.9 d10 5.6 R0 Infinity d0 1.2 n0 1.51743 R0'' < or = Infinity d0'' < or = 1.0 R11 -255.0 d11 1.1 n6 1.8411 Nu d6 43.3R12 12.65 d12 10.0 n7 1.54072 Nu d7 47.2R13 -10.8 d13 2.0 n8 1.53996 Nu d8 59.7R14 -18.8 d14 0.2 R15 20.0 d15 1.0 n9 1.6968 Nu d9 55.6R16 8.5 d16 2.3 R17 12.75 d17 3.8 n10 1.58065 Nu d10 37.1R18 -14.0 d18 1.05 n11 1.58313 Nu d11 59.3 R19 Infinity d19 1.2 R20 Infinity d20 6.4 n12 1.58065 Nu d12 37.1R21 -12.12 d21 2.2 R22 -13.9 d22 1.1 n13 1.86074 Nu d13 23.1R23 34.65 d23 0.7 R24 -75.0 d24 2.2 n14 1.44628 Nu d14 67.2R25 -10.75 d25 0.1 R26 466.0 d26 7.0 n15 1.52 Nu d15 70.0R27 -20.584 where f denotes the focal length of the enTire lens system, R denotes radius of curvature of each lens surface, d denotes center thickness of each lens and air spacing between adjacent lenses, n denotes refractive index of each lens for helium d spectro-ray, and Nu d denotes dispersive power of each lens for helium d spectro-ray.
 4. A retrofocus type lens system according to claim 1, which has the data as follows: f 16.4 B.f. 41.3F/5.6 Angle of field: 106* R1 39.7 d1 2.65 n1 1.732 Nu d1 53.2R2 26.8 d2 6.6 R3 37.1 d3 2.3 n2 1.732 Nu d2 53.2R4 25.9 d4 5.3 R5 41.9 d5 6.3 n3 1.732 Nu d3 53.2R6 409.0 d6 0.1 R7 24.45 d7 1.05 n4 1.8411 Nu d4 43.3R8 15.05 d8 2.06 R9 21.3 d9 1.4 n5 1.8411 Nu d5 43.3R10 14.1 d10 6.0 R11 -170.0 d11 11.0 n7 1.58065 Nu d7 37.2 R13 -13.7 d13 1.0 n8 1.58313 Nu d8 59.3R14 -19.22 d14 0.1 R15 22.1 d15 0.6 n9 1.6969 Nu d9 55.6R16 9.45 d16 2.55 R17 13.95 d17 4.1 n10 1.58065 Nu d10 37.1R18 -22.0 d18 1.0 n11 1.58313 Nu d11 59.3R19 1470.0 d19 1.4 R20 -7355.0 d20 5.9 n12 1.58065 Nu d12 37.1R21 -12.4 d21 0.6 R22 -13.6 d22 3.0 n13 1.86074 Nu d13 23.1R23 41.4 d23 0.7 R24 -60.0 d24 2.5 n14 1.51118 Nu d14 50.9R25 -11.1 d25 0.1 R26 1160.0 d26 9.5 n15 1.52 Nu d15 70.0R27 -24.75 where f denotes the focal length of the entire lens system, R denotes radius of curvature of each lens surface, d denotes center thickness of each lens and air spacing between adjacent lenses, n denotes refractive index of each lens for helium d spectro-ray, and Nu d denotes dispersive power of each lens for helium d spectro-ray.
 5. A retrofocus type lens system comprising the combination of: i. a divergent group forming the forward part of the lens system and including at least: a. a first pair of divergent components disposed at the foremost end of the lens system, each of said first pair of divergent components comprising a negative single meniscus lens having the convex surface thereof for direction toward an object, b. a first convergent component disposed behind said first pair of divergent components and comprising a single meniscus lens having the convex surface thereof for direction toward the object, c. a second divergent component disposed behind said first convergent component and comprising a single meniscus lens having the convex surface thereof for direction toward the object, and d. a second convergent component disposed behind said second divergent component and comprising a cemented meniscus lens assembly consisting of a biconcave lens and a biconvex lens disposed in the named order in the rearward direction and joined together, said cemented meniscus lens assembly as a whole having the concave surface thereof for direction toward the object; ii. a quasi-symmetric group disposed behind said divergent group and having a diaphragm disposed intermediately, said quasi-symmetric group comprising at least: e. a third divergent component forming the foremost part of said quasi-symmetric group and comprising a single meniscus lens having the convex surface thereof for direction toward object, f. a third convergent component disposed behind said third divergent component and just before said diaphragm, said third convergent component comprising a single lens having the convex surface thereof for direction toward the object, g. a fourth convergent component disposed just behind said diaphragm and comprising a single lens having the convex surface thereof for direction toward the image in such a manner that said convex surface is substantially symmetrical with said forward-looking convex surface of said third convergent component about said diaphragm, h. a fourth divergent component disposed behind said fourth convergent component and comprising a biconcave lens, and i. a fifth convergent component disposed behind said fourth divergent component and comprising a single meniscus lens having the convex surface thereof for direction toward the image in such a manner that said convex surface is substantially symmetrical with said forward-looking convex surface of said third divergent component about said diaphragm; and iii. a convergent group forming the rearmost part of the lens system and comprising at least one component consisting of a positive single lens having the convex surface thereof for direction toward image.
 6. A retrofocus type lens system according to claim 5, which has the data as follows: f 18.4 B.f. 37.52F/4 Angle of field: 100* R1 42.0 d1 2.0 n1 1.6968 Nu d1 55.6R2 27.9 d2 4.5 R3 37.8 d3 1.8 n2 1.6968 Nu d2 55.6R4 25.5 d4 4.5 R5 40.0 d5 5.0 n3 1.62041 Nu d3 60.3R6 250.0 d6 0.1 R7'' 24.6 d7'' 1.0 n4'' 1.6968 Nu d4'' 55.6R8'' 12.4 d8'' 7.0 R9 (omitted) d9 (omitted)n5 (omitted) Nu d5 (omitted)R10 (omitted) d10 (omitted)R11'' -200.0 d11'' 2.0 n6'' 1.77279 Nu d6'' 49.5R12'' 12.3 d12'' 12.0 n7'' 1.589 Nu d7'' 48.6R13'' -28.0 d13 (omitted) R14 (omitted) d14 0.1 n8 (omitted) Nu d8 (omitted)R15 23.8 d15 1.0 n9 1.67025 Nu d9 57.5R16 10.1 d16 2.6 R17'' 16.3 d17'' 5.95 n10'' 1.58065 Nu d10'' 37.1 R18'' Infinity d18 (omitted)R19 (omitted) d19 1.5 n11 (omitted) Nu d11 (omitted)R20'' Infinity d20'' 2.0 n12'' 1.58065 Nu d12'' 37.1R21'' -14.3 d21 4.6 R22 -14.6 d22 3.2 n13 1.86074 Nu d13 23.1R23 50.7 d23 0.9 R24 -38.5 d24 2.5 n14 1.51823 Nu d14 59.0R25 11.8 d25 0.1 R26 -
 7. A retrofocus type lens system according to claim 5, which has the data as follows: f 18.4 B.f. 37.54F/3.5 Angle of field: 100* R1 42.0 d1 2.0 n1 1.6935 Nu d1 50.6R2 28.0 d2 3.8 R3 37.8 d3 1.8 n2 1.6968 Nu d2 55.6R4 25.5 d4 4.5 R5 40.0 d5 5.0 n3 1.62041 Nu d3 57.5R6 280.0 d6 0.1 R7'' 24.6 d7'' 1.0 n4'' 1.6968 Nu d4'' 55.6R8'' 12.4 d8'' 7.0 R9 (omitted) d9 (omitted)n5 (omitted) Nu d5 (omitted)R10 (omitted) d10 (omitted) R11'' -200.0 d11'' 2 n6'' 1.77279 Nu d6'' 49.5R12'' 12.6 d12'' 12.0 n7'' 1.58267 Nu d7'' 46.5R13'' -27.8 d13'' (omitted) R14 (omitted) d14 0.1 n8 (omitted) Nu d8 (omitted)R15 23.8 d15 1.0 n9 1.67025 Nu d9 57.5R16 10.1 d16 2.55 R17 '' 16.3 d17'' 5.7 n10'' 1.58065 Nu d10'' 37.1R18'' Infinity d18 (omitted) R19 (omitted) d19 1.5 n11 (omitted) Nu d11 (omitted)R20'' Infinity d20'' 2.45 n12'' 1.58065 Nu d12'' 37.1R21'' -14.3 d21'' 4.4 R22 -14.6 d22 3.2 n13 1.86074 Nu d13 23.1R23 51.4 d23 0.95 R24 -38.5 d24 2.4 n14 1.51823 Nu d14 59.0R25 -11.78 d25 0.1 R26 -550.0 d26 8.5 n15 1.55671 Nu d15 58.5R27 -19.27 where f denotes the focal length of the entire lens system, R denotes radius of curvature of each lens surface, d denotes center thickness of each lens and air spacing between adjacent lenses, n denotes refractive index of each lens for helium d spectro-ray, and Nu d denotes dispersive power of each lens for helium d spectro-ray.
 550. d26 8.5 n15 -1.55661 Nu d15 58.5R27 -19.337 where f denotes the focal length of the entire lens system, R denotes radius of curvature of each lens surface, d denotes center thickness of each lens and air spacing between adjacent lenses, n denotes refractive index of each lens for helium d spectro-ray, and Nu d denotes dispersive power of each lens for helium d spectro-ray. 